The present invention relates to novel squaraine based dyes. More particularly, the present invention relates to squaraine based dyes with terminal aminoanthracene or acridinium units with absorption maximum above 700 nm of the formula 1 (1a, 1b, 1c) 
The present invention also relates to a process for the preparation of novel squaraine based dyes.
Squaraine dyes belong to a class of compound formed by the condensation reaction of different nucleophiles such as aniline or pyrrole with squaraine acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) Due to their unique properties, squaraine dyes are used in layered photo-responsive imaging, devices to extend the response capability of such devices to visible and infrared illumination These photo-responsive devices can therefore be utilised, for example, in conventional electrophotographic copiers as well as laser printers. These photoresponsive devices may comprise single or multilayered members containing photoconductive materials comprising squaraine compositions in a photogenic layer.
Photoconductive imaging members containing certain squaraine compositions are known. Also known are layered photoresponsive devices containing photogenerating layers and transport layers as described for example, in U.S. Pat. Nos. 4,123,270, 4,353,971, 3,838,095 and 3,824,099. Examples of photogenerating layer compositions disclosed in U.S. Pat. No. 4,123,270 include 2,4-bis(2-methyl-4-dimethylaminophenyl)-1,3-cyclobutadiene diylium-1,3-diolate, 2-4-bis-(2-hydroxy-4-dimethylaminophenyl)-1,3-cyclobutadine-diylium-1,3, diolate, and 2,4-bis-(p-dimetliylaminophenyl)1-3-cyclobutadine-diylium-1,3-diolate. Other patents disclosing photoconductive devices with squaraines are U.S. Pat. No. 6,042,980, U.S. Pat. No. 6,040,098, U.S. Pat. No. 5,342,719, U.S. Pat. No. 4,471,041, U.S. Pat. No. 4,486,520, U.S. Pat. No. 4,508,803, U.S. Pat. No. 4,507,480, U.S. Pat. No. 4,552,822, U.S. Pat. No. 4,390,610, U.S. Pat. No. 4,353,971 and U.S. Pat. No. 4,391,388.
Infrared absorbing dyes with high extinction coefficients are also useful for generating heat in the medium. In such a process exposure of the medium containing the dye to infrared actinic radiation of a frequency absorbed by the dye, results in generation of heat within parts of the medium exposed to the radiation. Materials, which undergo localized changes of state when, exposed to radiation of high energy density, e.g. laser light can be used in optical recording media. The thermally induced changes of state are associated with changes in the optical properties and are utilized for information and data recording. Use of squaraine dyes for such applications is described in U.S. Pat. No. 4,830,951. The medium may also comprise a thermally sensitive material capable of undergoing a colour change upon exposure to heat. Use of squaraine dyes for such applications is described in U.S. Pat. No. 4,623,896, U.S. Pat. No. 4,663,518, U.S. Pat. No. 4,720,449, U.S. Pat. No. 4,960,901 and U.S. Pat. No. 5,153,169.
Many of the known squaraine dyes are fluorescent compounds emitting light in the visible and near-infrared region. Consequently another use proposed for squaraine dyes is in the area of assays. Fluorescent compounds have achieved wide application in assays because of their ability to emit light upon excitation with light with energy within certain energy ranges. More specifically there is considerable interest in fluorescent dyes emitting in the near-infrared region. Such fluorescers have found employment as labels in chemical and biochemical processes. Fluorescent labels find applications in immunoassays, involving specific binding, pairs, such as ligands and receptors, for example, antigens and antibodies. Another use of fluorescent compounds is to incorporate such compounds into a cell wall or liposome. The cell or the liposome with the fluorescent compound incorporated therein can also be employed in assays. For example, dyes incorporated into cell membranes are usefull in the area of blood typing where a chance in fluorescence because of agglutination of cells is determined. Liposomes containing fluorescent dyes also find application in immunoassays. Furthermore such fluorescent compounds should be preferably soluble in aqueous medium or be at least water compatible.
Laser beams find use in the assay area as means for irradiating a fluorescent compound. In the filed of assays it is important to avoid background signals produced in relation to the amount of the analyte, contributed by materials other than the analyte. For example serum or plasma from a patient is often used to conduct the assay. Serum is itself fluorescent, however the materials in the serum or plasma that are fluorescent normally absorb light at wavelengths below 600 nm. Therefore it is desirable that the dyes employed in fluorescence assays possess absorption maximum greater than 600 nm, since the signal to noise ratio improves with increasing wavelength of absorption and emission of the dye. A major bottleneck in the complete utilization of near infrared absorbing dyes for such applications is that dyes absorbing in this region have low fluorescence quantum yields. Squaraine dyes synthesized sing aromatic heterocyclic for use in such applications have been described in U.S. Pat. No. 5,310,922; U.S. Pat. No. 5,329,019, and U.S. Pat. No. 5,416,214. However, the squaraine dyes described in these patents possess absorption and emission maxima below 700 nm.
Furthermore, several patents disclose processes for preparing squaraine compositions. For example, U.S. Pat. No. 4,5484,220 illustrates a squaraine forming process by the reaction of squaric acid, and an aromatic aniline in the presence of an aliphatic amine. In addition, a process for the preparation of squaraines by the reaction of an alkyl squarate, and an aniline derivative in the prescience of aliphatic alcohol, and an optional acid catalyst is described in U.S. Pat. No. 4,524,219. U.S. Pat. No. 4,524,218 discloses a process for the preparation of squaraines by the reaction of squaric acid with an aromatic amine, and a composition selected from the group consisting of phenols and phenol squaraines, which reaction is accomplished in the presence of an aliphatic alcohol, squaraines, which reaction is accomplished in the presence of an aliphatic alcohol, and an optional azeotropic catalyst. Other processes for preparing squaraines are illustrated in U.S. Pat. No. 4,525,592, which describes the reaction of dialkyl squarate, and an aniline derivative in the presence of an aliphatic alcohol and an acid catalyst. A method for synthesis of squaraines and intermediates for the synthesis of these compounds is described in U.S. Pat. No. 5,919,950. Process for preparation of squarylium dyes is also described in U.S. Pat. No. 5,656,750 and a method for making water soluble squaraine dyes is described in U.S. Pat. No. 5,625,062.
Novel unsymmetrical squaraines and methods for their preparation have been described in U.S. Pat. No. 4,521,621 and U.S. Pat. No. 5,030,537. Although the above squaraines, and processes thereof are suitable for their intended purposes, there continues to be a need for other squaraine dyes with strong absorption and emission characteristics beyond the 700 nm region. More specifically with regard to imagine devices, there remains a need for stable imaging dyes with certain stable physical and electrical characteristics, with improved sensitivity in the  greater than 700 nm region. Enabling the use of such dyes in different imaging and printing processes, including processes wherein diode lasers are used. New infrared dyes are needed which absorb at specific wavelength for such applications. Use of naptholactam squaric acid dyes which belong to a class of Squaraine dyes that contain hetrocyclic enamine type terminal groups in optical recording materials is described in U.S. Pat. No. 4,830,951. Squaraine dyes possessing tertiary arylamine end groups have the potential for better stability than those with the heterocyclic enamine type end groups. It has however hitherto not been possible to produce squaraine dyes containing tertiary arylamile end groups absorbing beyond 700 nm. Squaraine dyes containing aminothiophene terminal groups possessing absorption red shifted to that of squaraine dyes containing terminal dialkylaniline groups has been reported. The maximum absorption wavelength that could be observed was 705 nm [Kiel, D.; Hartmann, H.; and Moschny, T., Dyes and Pigments, 17,19,(1991)]. A squaraine derivative containing 2,3-dihydropyrimidine terminal groups with absorption in the 800 nm region has been reported [Glieter, R.; Pflasterer, G.; Nuber, B., J. Chem. Soc., Chem. Commun. 452 (1993); U.S. Pat. No. 5,625,062]. However these squaraine derivative contain secondary amines.
Also, there continues to be a need for new fluorescent dyes with improved absorption in the near infrared region, possessing long fluorescent lifetimes for application as biological probes for the analysis of DNA, lipids, peptides and proteins [Soper, S. A. Mattingly, Q.I., J. Am, Chem Soc. 116,3744, (1994)].
The main object of the present invention is to provide novel squaraine based dyes.
It is another object of the invention to provide a process for the preparation of squaraine based dyes containing tertiary amino anthracene.
It is a further object of the invention to provide novel squaraine dyes possessing high extinction coefficients in the near infrared region and hence useful as near infrared absorbed in thermal imaging processes.
A further object of the invention is to provide novel squaraine dyes useful inter alia as near infrared fluorescent labels for immunoassays
The aim of the present invention is to provide novel tertiary amino anthracene containing squaraine compositions and processes for the preparation thereof. The novel squaraine dyes and novel compositions containing such dyes have an absorption ranging from 650-820 nm with a maximum ranging from 780 to 800 nm and both lipophilic and hydrophilic dyes are reported in this invention. In addition, novel squaraine dyes with absorption maxima in the 900 nm region, containing acridine chromophores is also reported.
The compounds of the present invention can be prepared by a reaction sequence, some or all of the individual steps of which are separately known in the art. Most of the squaraine dyes of the present invention can be made according to procedures similar to those described in literature [Sprenger, H.-E., Ziegenbein, W. Angew, Chem. Int. Ed. Engl. 6,553, (1967); Sprenger, H.E-; Ziegenbein W. Angew, Chem Int. Ed Engl. 7,530 (1968); Schmidt. A. H. synthesis 961 (1980)]. In general, squaric acid (3,4-dihydroxy-3-cyclobutene-1,4-dione) is condensed with the aminoanthracene derivatives under conditions for removing water from reaction mixture and purifying the dye by crystallization or chromatography. The group or functionality imparting hydrophilicity or lipophilicity to the compound of the invention can be introduced into the aminoanthracene derivative before the condensation reaction.
The squaraine dyes of the patent can be conjugated to specific binding pair (sbp) members such as antigens and antibodies by techniques that are known in the art. On the other hand, a linking group as described above can be introduced to the squaraine dye or the sbp member for attachment to the other component. A functionality for attachment of carboxylic acid, hydroxyl, thio, amino, aldehydic, amido, activated ethylenes such as maleimide, sulfonic acid, and the like can be introduced into the squaraine dye or the sbp member if such functionality is not originially present in the dye. Methods of conjugation involving sbp members are described in e g. U.S. Pat. No. 3,817,837. The dyes produced by the processes of the present invention may be used in any of the applications in which prior art near infrared absorbers have been used. The dye can be used in printing inks intended to provide markings that can be read under near infrared radiation, for example, on packages of consumer items intended to be scanned by infrared laser scanners. The dyes may also be useful as charge transfer materials in xerography and electro photography.
The novel squaraine dyes described in the present investigation possess high extinction coefficients in the near infrared region and will hence be useful as near infrared absorbed in thermal imaging processes described in the U.S. Pat. No. 4,602,263 U.S. Pat. No. 4,826,976 and U.S. Pat. No. 4,830,951.
Accordingly the present invention provides novel squaraine dye containing terminal aminoanthracene or acridine groups represented by the formula 1 (1a, 1b and 1c) 
The present invention also relates to a process for the synthesis of a novel squaraine dye containing terminal aminoanthracene or acridine groups represented by the formula 1 (1a, 1b and 1c) 
said process comprising reacting squaric acid with an anthracene or an acridine chromophore in an organic solvent with simultaneous removal of water formed, cooling the reaction mixture, filtering and drying residue obtained, recrystallising the residue in an organic solvent to obtain a substantially pure product.
In another embodiment of the invention, the anthracene chromophore used comprises 1-N,N-dibutylaminoabnthracene.
In yet another embodiment of the invention, the acridinine chromophore used comprises 6-methylacridinium iodide.
In a further embodiment of the invention, the organic solvent used for the reaction is selected from 1-butanol, n-butanol, benzene, and a mixture thereof
In another embodiment of the invention, the acridine compound is reacted with squaric acid in the presence of a base comprising pyridine.
In another embodiment of the invention, the organic solvent used for recrystallisation comprises a mixture of chloroform and methanol in a ratio of 1:4.
The dyes are useful in imaging processes where absorption or near infrared radiation by the dye result, in acid generation in the medium as described in U.S. Pat. No. 5,286,612.
Yet another application of the dyes is its use as near infrared fluorescent labels for immunoassays.